In drum-type seed planters, seed is typically gravity-fed from a hopper to a revolving seed drum. A fan or blower provides air pressure which pressurizes the interior of the drum, and which also pressurizes the interior of the hopper to permit gravity-flow of seeds into the pressurized drum. The air pressure within the drum causes seeds to be picked up in perforated pockets formed in the periphery of the drum as the same rotates. The pocketed seeds are released as they pass by external seed-release wheels which block the perforations of the pockets and the passage of air therethrough. The seeds thereupon drop into delivery tubes positioned within the drum and are propelled by the pressurized air to be delivered into opened furrows. Examples of rotating drum seed planters are shown in U.S. Pat. Nos. 3,848,552, 3,860,146, and 3,885,704.
As shown in the said patents, the pressurization means of prior planters typically comprised a rotary blade fan or centrifugal blower mounted on the rear of the seed hopper and in communication with the planter drum. The fan was vertically oriented and various tubes and ducts were provided between the drum and hopper for achieving the desired equalized pressure in the hopper and drum. While that arrangement has been very commercially successful, it did not facilitate replenishment of the seed supply hopper. Specifically, when refilling of the seed hopper was required, it was necessary for the operator to remove the hopper cover and manually pour in seeds, or else attach some form of screw conveyor or the like connected to a bulk source of seeds.
More recently, efforts have been made to refill a seed hopper from a bulk source by creating a negative pressure or suction condition in the hopper. In general, those efforts involved complex and expensive tubing and valve arrangements attached to and external of the hopper. One example of such an arrangement is illustrated in USSR Patent No. 843,810, which shows a fan which can be connected to a seed bunker through a fan intake pipe which can be alternately opened to the atmosphere and the interior of the bunker. In that arrangement, however, the fan operates externally on pneumatic seed ducts positioned under the bunker, and thus the device is unsuitable for drum-type seed planters which require positive air pressure within the seed hopper for proper functioning.
There thus exists a need for a drum-type seed planter construction having simplified pressurization means operable for planting and for filling the seed supply hopper.